Efforts to understand the discrimination of time have proceeded along two relatively independent paths, one focusing on timing short intervals and one focusing on timing intervals of approximately a day. These efforts have studied different experimental manipulations and dependent variables, constructed different theoretical frameworks, and communicated findings to different research communities. These factors have led to the conclusion that the timing of short intervals and circadian rhythms are based on unrelated mechanisms. However, recent findings about the discrimination of short and circadian intervals suggest similarities in these two domains and raise the prospect of advancing the knowledge base of timing by examining the continuum of timing from short interval to circadian ranges. The long-range goal is to develop a theory of timing that encompasses the discrimination of temporal intervals across several orders of magnitude from milliseconds to days. The objective of this application is to exploit strong features of short interval and circadian approaches to identify mechanisms of short-interval time discrimination. The central hypothesis is that multiple oscillators, with periods that range from milliseconds to days, underlie time discrimination. The mechanism underlying local maxima in sensitivity to time will be examined in the short-interval domain. The working hypothesis is that each established local maximum in timing is based on an oscillator mechanism. Properties of oscillator and accumulator mechanisms will be tested by examining self-sustaining free-running rhythms, entrainment boundaries, and phase-response curves in short-interval timing. The relation between multiple local maxima in sensitivity to time will be determined. The working hypothesis is that a circadian oscillator synchronizes short-interval oscillators in a multi-oscillator system. Coupling between oscillators will be tested by correlating free-running periods in short-interval timing and manipulating the circadian system and testing properties of the short-interval system. The proposed research is expected to demonstrate (1) that local maxima in sensitivity to time are based on an oscillator mechanism, (2) the coupling relationship among multiple oscillators, and (3) that new mechanisms of time discrimination can be identified by integrating short-interval and circadian approaches. This integration is expected to have a major impact on short-interval and circadian fields because the current assumption of independence between these domains has not been tested and new advances will emerge from identifying common mechanisms.